Continuous industrial advancement is accompanied by a constant increase in global CO2 emissions, which leads to global warming as well as a high frequency of natural disasters [1]. Carbon capture utilization and storage (CCUS) technologies are believed as the possible way to effectively reduce atmospheric CO2 concentration in a short term [2]. Microalgae are single-celled organisms that can undergo photosynthesis in aquatic ecosystems and can grow under a wide range of environmental conditions with the higher growth rate and lipid content than conventional crops. As a result, they are regarded as the most effective plant microbes at absorbing CO2 and producing lipids through photosynthesis, serving as a prime source of raw materials for biofuel production and a prospective contender for both addressing CO2 emissions and energy shortages [3]. Furthermore, microalgae have potential significance in industries like aquaculture, food, and pharmaceuticals due to its high level of lipid, polyunsaturated fatty acids, and many active components [4,5].

Microalgae absorb and convert light energy via electron transport into a chemically stable form by the photosynthesis. Light energy is captured by antenna pigments in photosystem II (PSII) and photosystem I (PSI) and produce excited chlorophyll molecules (Chl*), called absorption (ABS). Part of the ABS can be trapped and channeled to the reaction center. The trapped energy flows through several medium electron transport complexes and participates in reducing QA to QA−, which will be finally oxidized by the accepter side of PSI. As a consequence, CO2 is fixed. Along with electrons transport, energy which cannot be utilized dissipates as heat and fluorescence. Based on this energy cascade, prompt fluorescence emitted by Chl-a reflects the photosynthetic activity, especially for PSII, and can be measured fast, non-invasively, precisely and inexpensively [6]. It can provide both qualitative and quantitative information on physiological state of photosynthetic apparatus [7,8].

Photosynthesis is highly sensitive to stress and often inhibited before other cell functions are impaired [9]. Many studies have shown that light quality plays a crucial role in microalgal metabolism. The effect of light wavelength on growth is species specific because different species have different metabolic routes, pigment deposition patterns, and photoreceptors [4,5,10,11,12]. The spectra of light were widely reported affecting the growth and metabolite biosynthesis in green microalgae Dunaliella salina, Nannochloris atomus, N. oculate, Botryococcus braunii, and Chlorella sp. [13,5,14,15,16,17]. Chlamydomonas reinhardtii and C. variabilis were reported regulating their light-harvesting functions through changing energy transfer pattern among pigment molecules in response to different light quality [18]. However, the effects of light quality on the photosynthetic electron transport and energy utilization efficiency of microalgal cells, which may regulate the biomass and substance accumulation of a culture, have not been sufficiently studied until now.

The salt-tolerant Dunaliella is a single-celled and double-flagellated green alga that exhibits unique characteristics in eukaryotic photosynthetic marine microalgae by synthesizing and altering intracellular glycerol concentration to allow it to grow over a very wide range of salt concentrations [19,20]. It is also an important source of natural antioxidants and biofuel production [5,21]. Due to its unique ability to adapt to high salt environments and light, it is also a model organism for studying domestication responses to abiotic environmental stress.

In this study, D. bardawil was cultured under monochromatic red and blue light, as well as their combinations with different ratios, while white light was used as the control. The effects of light quality on the growth and substance production of D. bardawil were investigated. Additionally, Chl-a fluorescence was employed to assess the photosynthetic performance simultaneously. Furthermore, an analysis was conducted to examine the relationship between substance production capacity and photosynthetic performance of D. bardawil.